Cholesterol absorption in human small intestine organ culture and rat small intestine epithelial cell culture IRD-98 has been studied using [14C] cholesterol, [3H] cholesterol and [14C] sitosterol. It has been found that cholesterol absorption is a dose- and time-dependent process, while sitosterol absorption is not and makes up to about 25% of the total cholesterol absorption. Cholesterol absorption appeared to be a specific process. The endocytosis inhibitor monensin decreased specific cholesterol absorption by 37%. Cholesterol absorption was examined under different conditions influencing cholesterol metabolism in the cell. Loading of IRD-98 cells with non-lipoprotein cholesterol caused a dose-dependent decrease of cholesterol absorption. The inhibitor of acyl coenzyme A:cholesterol acyl transferase (ACAT), compound Sandoz 58-035, had a similar effect on cholesterol absorption. Lovastatin, an inhibitor of 3-hydroxymethyl-3-glutaryl coenzyme A (HMG-CoA) reductase, stimulated cholesterol absorption in a dose-dependent manner. Loading of cells with cholesterol, lovastatin and Sandoz 58-035 had no effect on sitosterol absorption. The possibility has been demonstrated of using human small intestine organ culture and rat small intestine epithelial cell culture IRD-98 as models for studying cholesterol absorption.